This invention relates to the art of papermaking. More specifically, it relates to an improvement in one or two-wire, multi-ply papermaking forming apparatus wherein a lower looped forming wire is arrayed to have a diverging path of travel immediately downstream of a secondary headbox which projects a stock slurry stream onto the diverging path of forming wire travel. In some embodiments, a second, or upper, looped forming wire comes into co-running engagement with the lower forming wire to provide for the extraction of water from the stock slurry traveling between the co-running forming wires upwardly to within the upper forming wire and downwardly to within the lower forming wire.
Still more specifically, this invention relates to a specific configuration of the lower, or fourdrinier, forming wire relative to a secondary headbox slice opening whereby the lower forming wire is directed downwardly and away from the secondary headbox slice to effect a very low angle of impingement of the stock slurry onto the lower forming wire while simultaneously permitting the impingement of the stock slurry at a short distance from the slice.
Examples of prior art paper forming apparatus which this invention improves upon are illustrated and described in U.S. Pat. No. 4,146,424 (Justus) and 4,414,061 (Trufitt et al). In these patents, as well as in some embodiments of this invention, the formation of at least the first ply of the paper web is initiated at an upstream location on a horizontally traveling forming wire, such as is found in a conventional fourdrinier-type papermaking machine. A structural feature common to both of these prior art arrangements is that due to the need to provide an upper forming wire turning roll to bring the upper forming wire into co-running engagement with the lower forming wire over or before the lower wire turning roll, the headbox for projecting the stock slurry onto the lower forming wire cannot be located closer than slightly upstream of where the upper forming wire comes into co-running engagement with the lower forming wire element, usually a roll, which defines the end of the horizontal travel of the lower forming wire. The result is that the stock stream is deposited onto the horizontal, or non-downwardly diverging, portion of the lower forming wire. While these forming arrangements have their own attributes, they do not permit a headbox to discharge a stock slurry onto the lower forming wire at a low angle and at a short distance from the end of the headbox slice opening.